1. Field of the Invention
The present invention relates to a component mounting apparatus which is applied to the mounting of an electronic component onto an electronic circuit substrate, and more particularly, to a nozzle drop prevention device, which is installed in a mounting head equipped with a nozzle for picking up a component.
2. Description of Related Art
With the propagation of leadless electronic components (chip component) in recent years, the shape and size of components have been diversified, and in an electronic component mounting apparatus for mounting these electronic components, there have been demands for high-speed operation, high precision, high productivity, and high reliability.
A conventional electronic component mounting apparatus will be hereinafter described with reference to FIG. 7. In FIG. 7, the electronic component mounting apparatus comprises a mounting head 51 equipped with a nozzle for picking up an electronic component, a suction device 52 for attracting the electronic component with the nozzle, an XY robot 53 for moving the mounting head 51 in the X and Y directions, and a control device 54 which controls actions of the mounting head 51, the suction device 52, and the XY robot 53. It is noted that FIG. 7 shows only the main elements of the mounting head 51, and illustration of, for example, a body part is omitted.
Reference numeral 55 represents a spline shaft, to which two nuts 56, 57 are coupled such as to be movable in a direction of its axis. These nuts 56, 57 are supported in the body part (not shown) of the mounting head 51 via bearings 58, 59, respectively. By this construction, the spline shaft 55 is movable in the direction of its axis as well as rotatable around its axis, and it is driven to rotate by a motor 60 mounted on the mounting head 51 via a pulley 61, belt 62, and another pulley 63.
At the distal end 55a of the spline shaft 55 is mounted a nozzle 65 is mounted for picking up the electronic component 64. Inside the nozzle 65, a filter 66 is provided for preventing dust from entering into the nozzle when a suctional force. The spline shaft 55 is to be pushed upwards by a compression spring 68 via a bearing 67 which is slidable in a circumferential direction, and by applying a pressing force from a voice coil motor 69, the spline shaft 55 or the nozzle 65 is lowered to perform pick up and mounting actions of the electronic component 64.
The actions of the component mounting apparatus with the above described construction will be explained. The control device 54 activates the XY robot 53 to move the mounting head 51 to a component pick-up position where the electronic component is picked up. Then, by the control of the control device 54, the voice coil motor 69 is driven so as to compress the compression spring 68, by which the nozzle 65 is lowered via the spline shaft 55, and at the same time the suction device 52 is driven so that the nozzle 65 picks up the electronic component 64 by suctional force. Next, the nozzle 65 is lifted by means of the voice coil motor 69. The XY robot 53 is then driven to move the mounting head 51 to a component mounting position above the circuit substrate, after which the nozzle 65 is lowered by means of the voice coil motor 69 so that the electronic component 64 is mounted on the circuit substrate. When the power source is off or at the time of a power failure, the pressing force is not applied from the voice coil motor 69, and thus the spline shaft 55 or nozzle 65 is prevented from dropping due to the force of the compression spring 68 which is pushing the bearing 67 upwards.
However, in the above described construction, since the spline shaft 55 is urged upwards by the force of the compression spring 68, the voice coil motor 69 needs to have a pressing force greater than the force of the compression spring 68 alone wherefore there is a problem that precise control of pressing force for the mounting purpose cannot be achieved. Also, the voice coil motor 69 needs to have a capacity greater than necessary, thus causing the size of the voice coil motor or the mounting head 51 to become bulky. Furthermore, in order for minimizing the change of the compression spring 68 due to compression, it is necessary to make enough room for the compression spring 68, whereby the mounting head 51 becomes elongated in a vertical direction.